Indexing gear train for on-load tap changers of step transformers

ABSTRACT

The invention relates to an indexing gear train ( 10 ) for an on-load tap changer or tap selector of a step transformer, wherein at least one cam disk ( 18; 20 ) driven by a crank mechanism ( 12 ) interacts with an out-put disk ( 22 ) having engagement elements ( 24 ) arranged on the output disk, the output disk being connected to a switch shaft ( 40 ) in a rotationally fixed manner, wherein the at least one cam disk ( 18; 20 ), in interaction with the engagement elements ( 24 ) of the output disk ( 22 ), triggers an incremental rotation of the switch shaft ( 40 ) by a defined increment angle. The engagement elements ( 24 ) are formed by rollers ( 26 ) rotatably supported on a flat side near the outer circumference of the disk ( 22 ). Said rollers roll with a corresponding engagement contour on the outer surface of the cam disk ( 18; 20 ), said engagement contour having convex and concave cam sections ( 30; 42 ) that regularly follow each other and transition into each other.

The present invention relates to an indexing transmission for on-load tap changers of tapped transformers with the features of the independent patent claim.

Indexing transmissions of that kind or similar are disclosed by, for example, DE 26 08 051 A which shows a preselector, as well as by U.S. Pat. No. 2,785,242 A, which shows a so-called turning arrangement. In this known constructional form of indexing transmissions it is necessary to provide suitable mechanical means for end position blocking. These end position blocking means have to reliably prevent the possibility of movement beyond the end positions of the tap selector or on-load tap changer, which would normally lead to significant damage of the tap selector.

In addition, DE 10 39 129 A discloses a mechanical end position block in which a separate blocking disc, which is coaxially connected with a control disk for actuation of the tap selector, co-operates with a pawl which in turn can be actuated via intermediately arranged mechanical means by the control disc. This end position block is mechanically complicated and, moreover, unsuitable for blocking two mutually independently movable Maltese wheels arranged concentrically one above the other.

DE 23 39 973 A shows an arrangement in which an abutment is disposed on the Maltese cross and which at the appropriate instant actuates a turning arrangement or preselector by way of a lever system.

DE 40 09 503 C2 discloses a further development of an indexing transmission for tap selectors of tapped transformers, in which two Maltese wheels are arranged concentrically one above the other on a common tap selector axis and are driven by a Maltese crank having an upper and a lower entrainer pin. These two entrainer pins are offset relative to one another through 180 degrees and engage in roller slots of the respective Maltese wheel. In addition, one Maltese wheel co-operates with a turning abutment, by which a turning lever, which is pivotably arranged on the shaft, for actuation of a turning means or preselector is pivoted at a specific point of the switching sequence. Arranged on the turning lever is a blocking plate which is displaceable by means of a slot on the shaft carrying the turning lever.

An object of the present invention consists in proposing an indexing, which operates reliably and with as low friction as possible and/or with easy running, for an indexing transmission of an on-load tap changer or tap selector of a tapped transformer, in which the driven element is reliably fixed in its respective operational setting.

This object of the invention is achieved by the subject of the independent patent claim. Features of advantageous developments of the invention are evident from the dependent claims. In order to achieve the object of the invention the present invention proposes an indexing transmission for an on-load tap changer, tap selector or comparable switch of a tapped transformer, in which at least one cam disc, which is driven by way of a spring energy store, co-operates with a drive output disk with engagement elements arranged rotatably mounted thereon. This drive output disk is connected by the engagement elements rotatably mounted thereon with a switch shaft to be secure against relative rotation. This arrangement serves the purpose of allowing the cam disk in co-operation with the engagement elements of the drive output disk to trigger a stepped rotation of the switch shaft through a defined step angle. The present invention provides that the engagement elements are respectively formed by rollers which are rotatably mounted at a flat side in the vicinity of the outer circumference of the disk and which roll on the outer circumferential surface of the at least one cam disk by a corresponding engagement profile with convex and concave cam sections in regular succession and transitioning one into the other. Such a configuration forms a roller pair in which the engagement elements constructed as rollers roll on the outer circumferential surface, which forms an alternatingly curved cam, of the cam disk without appreciable sliding movements with accompanying friction effects then occurring. By comparison with a previously used Maltese transmission the significant advantage arises of a very easy-running reciprocal drive transmission with at the same time a very reliable function safe against jamming. The indexing transmission according to the invention enables blocking of the disks with the rollers arranged thereon after each indexing in a desired or definable angular position corresponding with a defined operational setting. For this purpose, the rollers roll on suitably profiled blocking cams of the cam disks or cam disc.

In the indexing transmission according to the invention selectably two, three or more engagement elements or rotatable rollers can be arranged, in respectively, uniform angular pitch at the outer circumference of the drive output disc. These rotational axes of the rollers are usefully oriented parallelly to the rotational axis of the disk and thus also of the switch shaft so that an easy-running and reliably functioning indexing transmission with an angular pitch defined in correspondence with the selected number of rollers and the distribution thereof at the outer circumference of the disk is formed. The outer profile of the cam disk and its outer circumferential surface, which is concave at least in a section, are preferably so designed that during the indexing the respective roller can roll substantially free of play in the concave cam section at the circumference of the cam disk whilst in the blocked position a further movement is reliably prevented by the intersecting circumferential circles of the drive output disk and the cam disk and the blocking thereof by two adjacent rollers.

With the transmission arrangement according to the invention it is possible to achieve fixing of the disks in the respectively achieved angular position after each indexing of the cam disk through a defined rotational angle. The primary objective of the indexing transmission according to the invention is not the position-blocking, but the particularly reliable and very easy-running and low-friction indexing function. Since the known and previously used friction lock is dispensed with in favor of a roller lock, a very precisely switching rotary transmission, which operates without appreciable friction, with an indexing function is made available. The transmission function formed by the indexing transmission can be influenced within certain constructional limits by the profiling of the cam disk or the plurality of cam disks and/or the placing or number of the rollers arranged at the disc.

For example, in the case of a design with six rollers uniformly distributed at the circumference of the disk drive output angles of 60° or 120° can be realized by means of drive angles of approximately 80° to 120° depending on the respectively desired translation ratios. Equally conceivable is influencing of the characteristics of the transmission function itself for the same ratio of drive angle to drive output angle, in that, for example, a polynomial of 5th order or a sloping sinusoidal line of the like is used. Moreover, it is possible to achieve almost any drive output angle if no two successive actuations are required in, respectively, the same direction.

In a further preferred variant of the indexing transmission a pair of cam disks arranged coaxially or axially parallel to one another with respectively substantially the same size and external profile are arranged offset relative to one another secure against rotation on the shaft coupled with the crank transmission. This pair of cam disks is disposed in operative engagement with a corresponding pair of disks, which are arranged concentrically on the switch shaft and offset relative to one another, with engagement elements mounted thereon. The disks and cam disk respectively disposed in operative engagement with one another are preferably identically constructed and dimensioned in paired manner and respectively arranged offset relative to one another on the associated shafts thereof in such a manner that a constrained guidance of the rollers and outer profiles of the cam disks rolling together is provided. The disk with the rollers mounted thereon can be further rotated only if the matching concave cam section is rotated into a position at the respective cam disk in order to accept a roller. The flowing transitions from the larger diameter of the cam disk to the concave receiving profile, which is formed as a recess with smaller diameter and which is preferably matched by the inner profile thereof and by the inner radius thereof to the diameter and profile of the corresponding rollers, then enables, on corresponding rotation of the cam disc, stepped movement of the drive output disk as well as of the switch shaft connected therewith to be secure against relative rotation. In order to enable these desired movements of the shafts arranged parallel to one another the external profiles of the cam disks preferably roll substantially free of play or with a small radial play against the outer circumferential surfaces of the rotatably mounted rollers or engagement elements of the disk or disks.

As also made clear on the basis of the exemplifying embodiments described in the following the driving element of the indexing transmission according to the invention is formed from two cam disks arranged one above the other. The driven element is formed from two planes of the disk respectively with six rollers uniformly distributed at the outer circumference. The cam disks engage, during the switching over process, in the plane associated therewith and move the driven element in substantially jolt-free manner from one detent setting or operational setting to the next. The rollers of the driven element in that case roll low in play on the respective cam flanks, which are respective sub-sections of a continuous overall cam formed from a plurality of convex and concave sections.

An alternative variant of the indexing transmission according to the invention can provide that the cam disk has at least one blocking pin, which is arranged at its end face in the vicinity of its outer circumference and which co-operates with a star wheel with a plurality of circumferential cam sections, the start wheel being connected with the switch shaft to be secure against relative rotation and arranged concentrically with respect to the disk with the engagement elements. In this variant of the indexing transmission only one set of disk and cam disk disposed in is operative engagement with one another is required, since the above-explained second disc, which co-operates with a second cam disc, is replaced by the pins which are arranged at the cam disk and which can engage in the star wheel connected with the switch shaft to be secure against relative rotation. The pitch of this star wheel, which has relatively deep engagement pockets for receiving the pin or the plurality of pins, is advantageously matched to the number of engagement elements or rollers present. Thus, for example, when three rollers are present also three engagement pockets at the star wheel are required so that this can fulfil the desired function. The mentioned star wheel in its profile vaguely resembles the Maltese disks known from the prior art, but by comparison with these fulfils a changed task, since it is merely supporting with respect to positioning of the disk relative to the rotating cam disk in order to be able to position the disk precisely in the desired angular steps and further rotate it. For this purpose the cam disk can have a respective blocking pin on either side adjacent to a circumferential concave cam section, wherein this concave cam section co-operates with one of the engagement elements or rotatable pins of the disk and the two blocking pins co-operate with the concave cam sections of the star wheel.

The desired switching steps are realized by means of the indexing transmission according to the invention in that the cam disk in non-blocked, rotating state rolls by its outer circumferential surface substantially free of play simultaneously against two engagement elements or rotatable pins of the disc. A is useful variant of the indexing transmission can, for example, be so constructed that the concave cam sections of the cam disk and the corresponding engagement elements or rotatable pins of the disk connected with the switch shaft to be secure against relative rotation each have a 120° pitch. Three rollers arranged uniformly at the circumference of the disk and optionally concave cam sections for the blocking pins are required for such a variant. However, other pitch steps are selectably also possible, in which two, four or, for example, five or more rollers are arranged in uniform distribution over the circumference of the disc.

The invention is explained in more detail in the following by way of embodiments with use of the drawing described in the following, in which:

FIG. 1 shows a perspective view of one variant of embodiment of an indexing transmission according to the invention,

FIG. 2 shows a plan view of the indexing transmission according to FIG. 1, FIG. 3 shows a side view of the indexing transmission according to FIG. 1,

FIG. 4 shows a further perspective view of the indexing transmission according to FIG. 1,

FIG. 5 shows a schematic plan view of an alternative variant of embodiment of an indexing transmission according to the invention,

FIG. 6 shows a perspective view of the indexing transmission according to FIG. 5 and

FIG. 7 shows a further perspective view of the indexing transmission according to FIG. 5.

The embodiments described in the following are not to be understood as restrictive with respect to the indexing transmission according to the invention, but serve for explanation of the function and the switching possibilities of the indexing transmission.

The illustrations of FIGS. 1 to 4 show in several views a first variant of embodiment of an indexing transmission according to the invention, which is denoted generally by the reference numeral 10. Such an indexing transmission 10 is used particularly in on-load tap changers (not illustrated) of a tapped transformer (here similarly not illustrated) in order to thereby activate and/or switch over tap switches, which are known per se, with mechanical switching elements and/or vacuum switching tubes. The indexing transmission 10 comprises a crank transmission 12 and at least one energy store 14, which is coupled therewith and which in the illustrated embodiment is provided with a helical spring 16 loaded in tension and/or compression. The crank transmission 12 is coupled by way of a shaft 13 with a pair of cam disks 18 and 20, which co-operate with and operatively engage a disk 22 with engagement elements 24 arranged to be rotatably mounted thereon. These engagement elements 24 are respectively formed as rollers 26 rotatably mounted on the disk 22 in the vicinity of the outer circumference thereof. The disk 22 together with the engagement elements 24 or rollers 26 rotatably mounted thereon is connected with a switch shaft to be secure against relative rotation. Of this rotationally fast connection, merely one drive output gear wheel 28 is shown in the illustrated embodiment.

The illustrated transmission arrangement serves the purpose of allowing the cam disks 18 and 20 in co-operation with the engagement elements 24 or rollers 26 of the disk 22 to trigger a stepped rotation of the disk 22 and thus the switch shaft through a defined step angle, here, for example, 60° in the case of six rollers 26 present at the outer circumference of the disk 22. The rollers 26 rotatably mounted on the two flat sides in the vicinity of the outer circumference of the disk 22 can engage in corresponding trough-shaped or concave cam sections 30 at the outer circumferential surface of the respective cam disk 18 or 20. In this roll pairing the rollers 26 roll on the outer circumferential surface of the cam disks 18 and 20, in which case very low friction arises.

In the case of the illustrated indexing transmission 10, in total six rotatable rollers 26 or engagement elements 24 are arranged at a regular angular pitch at the outer circumference of the disk 22. The axes of rotation of the rollers 26 are oriented parallelly to the axis of rotation of the disk 22 and thus also of the switch shaft so that an easy-running and reliably functioning indexing transmission 10 with an angular pitch of respectively 60 degrees defined in correspondence with the selected number of rollers 26 and the distribution thereof at the outer circumference of the disk 22 is formed. The outer profile of the cam disks 18 and 20 with the respective at least one concave cam section or segment 30 formed therein is so designed that during the switching step the rollers 26 can roll substantially free of play in the concave cam section 30 at the circumference of the respective cam disk 18 or 20, whilst in the blocked position or in the detent setting a further movement can be prevented by the intersecting circumferential circles of the disk 22 and cam disk 18 or 20 and the blocking thereof by two adjacent rollers 26. The disk 22 with the rollers 26 mounted thereon can be further rotated only when the matching recess pocket 30 at the respective cam disk 18 or 20 is rotated into a position in order to receive a roller 26. The flowing transitions from the larger diameter of the cam disk 18 or 20 to the concave cam section 30 formed as a recess with smaller diameter as well as to the web 32 of greater diameter adjoining thereat, wherein the concave cam section 30 and the transition to the web 32 are matched by the profiles thereof to the diameter and the profile of the corresponding rollers 26, then enable, with corresponding rotation of the cam disk 18 or 20, stepped movement of the disk 22 as well as of the switch shaft coupled therewith. In order to enable these desired movements of the shafts arranged parallelly to one another the outer profiles of the cam disks 18 and 20 can roll substantially free of play or with small radial play against the outer circumferential surfaces of the rotatably mounted rollers 26 or engagement elements 24 of the disk 22.

The illustrations of FIGS. 5 to 7 show several views of an alternative variant of embodiment of the indexing transmission 10 according to the invention. In this variant of the indexing transmission 10 the cam disk 18 has two blocking pins 34 which are arranged at the end face thereof in the vicinity of the outer circumference thereof and which co-operate with a star wheel 36 with a plurality of circumferential concave cam sections or cam segments 38. The star wheel 36 itself is connected with the switch shaft 40 to be secure against relative rotation and in the illustrated embodiment at the same time forms the disk 22 with the engagement elements 24 or rollers 26 arranged thereat. In this variant of the indexing transmission 10 only one set of disk 22 or star wheel 36 and cam disk 18, which are disposed in operative engagement with one another, is required, since the above-explained disk with rollers 26—which are arranged at both sides and which co-operate with a pair of cam disks—is redundant by virtue of the pins 34 arranged at the cam disk 18. The pins 34 can respectively engage in the concave cam sections 38 arranged on both sides near each roller 26. The pitch of this star wheel 36, which has concave segments 38 formed to be relative deep for reception of the pins 34, is advantageously matched to the number of engagement elements 24 or rollers 26 present. Thus, for example, in the case of the three rollers 26 which are present also three pairs of concave cam sections 38 are required at the star wheel 36 so that this can fulfil the desired function.

The cam disk 18 has between the two adjacent blocking pins 34 a concave cam section 42 which co-operates with the engagement elements 24 or rotatable rollers 26 of the disk 22 or star wheel 36, wherein in the case of appropriate positioning of the cam disk 18 and the star wheel 36 the two blocking pins 34 simultaneously co-operate with and engage the concave cam sections 38 of the star wheel 36. The desired switching steps are realized in that the cam disk 18 in the non-blocked, rotating state in correspondence with FIG. 5 rolls by its outer circumferential surface substantially free of play simultaneously against two rotatable pins 26 of the disk 22 or the star wheel 36. The concave cam sections and the corresponding rotatable rollers 26 of the star wheel 36 connected with the switch shaft 40 to be secure against relative rotation respectively have a 120° pitch. This variant accordingly has three rollers 26 uniformly arranged at the circumference of the star wheel 36 and corresponding cam segments 38 for receipt of the blocking pins 34. However, other pitch steps are selectably also possible, in which two, four or, for example five or more rollers are arranged in uniform distribution over the circumference of the disc. 

1. An indexing transmission for an on-load tap changer or a tap selector of a tapped transformer, in which at least one cam disk, which is driven by way of a crank transmission, co-operates with a drive output disk with engagement elements arranged thereon, the drive output disk being connected with a switch shaft to be secure against rotation relative thereto, wherein the at least one cam disk in co-operation with the engagement elements of the drive output disk triggers a stepped rotation of the switch shaft through a defined step angle, wherein the engagement elements are formed by rollers, which are rotatably mounted at a flat side in the vicinity of the outer circumference of the disk and which roll on the outer circumferential surface of the cam disk by a corresponding engagement profile with convex and concave cam sections in regular succession and transitioning into one another.
 2. The indexing transmission according to claim 1, wherein two, three or more engagement elements or rotatable rollers are respectively arranged at regular angular pitch at the outer circumference of the disk and co-operate with the cam sections of the cam disk.
 3. The indexing transmission according to claim 1, wherein the at least one drive output disk is, after each indexing of the cam disk through a defined rotational angle, fixed in the respectively attained angular position.
 4. The indexing transmission according to claim 1, wherein a respective pair of cam disks, which are arranged coaxially or axially parallel to one another, with respectively substantially the same size and outer profile are arranged rotationally fixed relative to one another at the shaft coupled with the crank transmission, which are disposed in operative engagement with a set of engagement elements which are coupled coaxially or axially parallelly with the switch shaft and arranged to be offset to relative to one another and which are rotatably mounted on the disk.
 5. The indexing transmission according to claim 1, wherein the outer profiles of the cam disks roll substantially free of play or with small radial play against the outer circumferential surfaces of the rotatably mounted rollers or engagement elements of the at least one disk.
 6. The indexing transmission according to claim 1, wherein the cam disk has at least one blocking pin, which is arranged at the end face thereof in the vicinity of its outer circumference and which co-operates with a disk, which is constructed as a star wheel, with a plurality of circumferential concave cam sections in the circumferential outer profile of the disk, which is connected with the switch shaft to be secure against relative rotation, wherein the disk or the star wheel carries the engagement elements.
 7. The indexing transmission according to claim 6, wherein the cam disk has a respective blocking pin on either side adjacent to a circumferential concave cam section, wherein the concave cam section co-operates with one of the engagement elements or rotatable pins of the disk and the two blocking pins co-operate with the concave cam sections of the star wheel
 8. The indexing transmission according to claim 1, wherein the cam disk in the non-blocked, rotating state rolls by the outer circumferential surface thereof substantially free of play simultaneously against two engagement elements or rotatable pins of the disk, whereby this is blocked in its rotation.
 9. The indexing transmission according to claim 1, to wherein the concave cam sections of the star wheel and the corresponding engagement elements or rotatable pins of the disk connected with the switch shaft to be secure against relative rotation each have a 120° pitch.
 10. The indexing transmission according to claim 1, wherein the rotational movements, which are triggered by the cam disks, of the disk or the star wheel are movable substantially jolt-free from one detent setting to the next. 